1. Technical Field
The present disclosure relates to a platen gap adjustment mechanism and to a printer having the platen gap adjustment mechanism.
2. Related Art
In order to print on a page in a booklet, such as a passbook, the booklet is opened to expose the page to be printed on. The open booklet is then conveyed along a media conveyance path past a platen, and a printhead prints on the exposed page as the booklet passes the platen. The thickness of the open booklet therefore changes when the page to be printed on changes, i.e., when the booklet is opened to a different position. More specifically, the thickness of the print medium conveyed over the platen varies and depends upon the print job.
If the printer has a constant platen gap between the printhead and the platen, print quality might drop when the thickness of the print medium changes because the gap between the printhead and the print medium changes. Printers having a platen gap adjustment mechanism that moves the printhead vertically according to the thickness of the print medium conveyed over the platen are therefore used when print media of different thicknesses are used.
A printer with a platen gap adjustment mechanism is described in Japanese Unexamined Patent Application Publication JP-A-H09-202017. The printer in JP-A-H09-202017 enables a carriage that carries the printhead to pivot about the axis of a carriage guide shaft that supports the carriage. The carriage pivots up and down according to the thickness of the print medium by causing the bottom surface of the carriage to slide over the print medium passing the platen, thus causing the printhead to move vertically and suppressing variation in the gap between the printhead and the print medium.
The inventor(s) has recognized that, in the printer described in JP-A-H09-202017, the carriage tilts when the carriage pivots up or down from the reference position according to the thickness of the print medium, and the printhead carried on the carriage therefore becomes tilted relative to the printing surface of the print medium passing over the platen. When using a serial impact dot matrix printhead, which prints by striking an ink ribbon with the recording wires of the printhead and transferring ink from the ink ribbon onto continuous paper used as the print medium, print quality might drop when the printhead becomes inclined to the printing surface because the distance the recording wires (printing pins) travel to the printing surface changes.
If the platen gap adjustment mechanism has a lift mechanism that moves the carriage guide shaft vertically, and moves the carriage guide shaft up or down based on the thickness of the print medium passing the platen, the printhead mounted on the carriage can be moved up and down without tilting relative to the printing surface of the print medium. In this configuration, the carriage guide shaft, carriage, and printhead are moved up and down together, i.e., the weight of the driven members increases, and a motor or another drive unit might be used as the lifting mechanism. A sensor for detecting the thickness of the print medium might also be used which might complicate the device configuration and control or lead to an increase in the manufacturing cost of the printer.